Preliminary studies in rhesus macaques (RM) reveal that animals experimentally infected with the simian immunodeficiency virus (SIV) and rhesus rhadinovirus (RRV) develop B cell hyperplasia compared to RM infected with SIV alone. RRV, like Kaposi's sarcoma-associated herpesvirus (KSHV), encodes an interleukin-6 (IL-6) homologue, which is thought to be a necessary growth factor for Kaposi's sarcoma and the B cell- derived malignancy referred to as body cavity based lymphomas or primary effusion lymphoma in AIDS patients also infected with KSHV. The long-term objectives of this study aim to evaluate the role of the RRV vIL-6 homologue in viral-mediated B cell hyperplasia in the context of an SIV infection. Preliminary studies provided in the application strongly suggest that RRV vIL-6 is involved in RRV-associated disease, and as such provides an extremely value animal model to define the role of the viral encoded IL-6 in virus-mediated pathogenesis and to evaluate a novel therapeutic approach, utilizing a recombinant vIL-6-Fc fusion protein to induce anti-RRV vIL-6 responses to inhibit disease progression. To address this, the following Specific Aims are proposed: Specific Aim 1: Vaccinate immunocompetent and immunodeficient RM with vIL-6-Fc fusion protein (vIL-6-Fc) and characterize the host immune response. Studies include characterization of the humoral response by enzyme linked immunosorbent assays (ELISA) and neutralization assays, and characterization of T cell response, both CD4 and CD8, by intracellular cytokine stain or by ELISPOT. Specific Aim 2: Characterize host response to RRV infection in vIL-6-Fc vaccinated animals, both immunocompetent and immunodeficient. Studies involve those RM utilized in Specific Aim 1, and include experimental infection of SIV-infected RM with a novel RRV that encodes nonsense mutations in vIL-6 to evaluate the role of vIL-6 in RRV-associated disease compared to that of vaccinated animals infected with wild type RRV. Specific Aim 3: Define therapeutic potential of vIL-6-Fc vaccination in animals infected with SIV and RRV. Experiments include therapeutic vaccination of SIV/RRV-infected animals with vIL-6-Fc. Parameters that will be measured include: viral load as defined by co-culture analysis and real time PCR;differential leukocyte counts in peripheral blood;serum protein electrophoresis for hypergammaglobulinemia;host and viral IL-6 by ELISA and bioassay;lymph node and bone marrow biopsies, and physical examination. PUBLIC HEALTH RELEVANCE The incidence of KSHV infection and KSHV-associated disease in the developing and developed world will continue to grow as the population becomes immunodeficient due to HIV-1 infection or iatrogenic agents associated with organ transplantation. The results from the proposed studies utilizing the nonhuman primate animal model should help elucidate the role of the vIL-6 in virus infection and disease, and provide new insights into the future development of therapies for KSHV-associated LPD.